This invention relates to molds, more particularly to molds used in blow molding which allow a flashing seam to be moved to an inconspicuous location.
Molding is a process used to form substances into desired shapes. Typically a metal or plastic substance, in a fluid state, is placed into a mold by gravity or mechanical force. Most molds consist of two or more blocks, which are separated after the substance has solidified. The finished part is removed from the mold and the molding process is repeated.
Plastics may be molded using a variety of processes including blow molding, injection molding, compression molding, transfer molding, and rotational molding. Blow molding is basically a bulging process. A tubular piece of plastic is heated and then pressurized internally and expanded into the cavity of a relatively cool mold. Typical blow molded products are hollow, thin-walled containers or articles.
One drawback of any molding process is the by-product of flash, a thin layer of material, which is formed within the gap between the mold blocks. Flash is removed from finished parts, often in a subsequent manufacturing operation, but typically a seam remains on the part in the area where the flash originated. Flash seams may not be desirable in ornamental molded products.
Relocation of flash seams can be difficult depending upon the shape of the molded part and correspondingly, the shape of the interior surface of the mold blocks. A part having convex surfaces will have predictable flash seam locations if one of the convex surfaces is aligned with the interior mold surface where the mold blocks meet. The seam must be at the apex of this convex surface in order to allow the finished part to be ejected from the mold.
Removing undesired flash during the molding operation with the use of flash retainer in the mold is the subject of U.S. Pat. No. 5,480,607. This method has the drawback of still leaving a seam in a conspicuous location. Inserts have also been used previously in mold cavities. Inserts have been used to apply designs, such as dates arid codes to the surface of the molded product (U.S. Pat. No. 5,736,168) and used to achieve small variations in the shape of the molded product without the requirement of manufacturing an entirely new mold (U.S. Pat. No. 5,560,939). Inserts have also been used to sheer and seal ends of a parison in a blow mold (U.S. Pat. No. 4,032,278). These inventions do not allow or teach moving the flash seam on a molded product for ornamental reasons.
A mold, having inserts, which can relocate the flash seam to an inconspicuous location is desired.
The present invention overcomes disadvantages in the prior art by providing an improved mold. The invention provides in one aspect a mold which allows flash seams to be placed in an inconspicuous location comprising two or more mold blocks where a first block has a contact surface, which partially defines the shape of a molded part, a seating surface and a mating surface. A second block half has a contact surface, a sheer surface and a mating surface which abuts the mating surface of the first mold block when the mold is closed. The mold also has removable inserts having contact surfaces, which in conjunction with the mold block contact surfaces define a mold cavity, and having sheer edges which are apposed to the sheer surface of the second mold block. The inserts are seated upon the seating surface of the first mold block and restrict removal of a molded part by overhanging the mold cavity.
The invention provides in another aspect a method for displacing a flash seam away from a point of greatest width of a molded part, comprising extending a parison between a first mold block having a seating surface upon which an insert assembly is placed and a second mold block. The first mold block and second. mold block are brought together. In a subsequent step the parison is inflated with air to form a part. The point of greatest width of the part is located where the insert assembly rests upon the seating surface of the first mold block, yet a flash seam is formed between the insert assembly and the second mold block.